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Understanding and Defeating Feline Infectious Peritonitis (FIP) Part 1 of 5

NOTE: FIP treatment is rapidly changing. Please visit Cornell Feline Health Center, EveryCat Health Foundation, FIP Warriors 5.0 and University of California Davis Koret Shelter Medicine Program for the most up-to-date information.

Feline Infectious Peritonitis (FIP) was first described in the late 1950s by Dr. Jean Holzworth at Angell Memorial Animal Center in Boston. There’s a lot to know about this dreaded disease, and it starts by discussing Feline Coronavirus (FCoV), a highly contagious virus that’s found worldwide in domestic and wild cats; 80-85% of cats have been exposed to the virus. It’s FCoV that may mutate within a cat and develop into FIP, which until recently was considered fatal.

Kittens drink the first secretions of antibody-rich colostrum present in their mother’s milk 12-24 hours after birth. This antibody protection from mom lasts for 6-8 weeks. It’s not until at least 12-16 weeks of age that kitten immune systems are mature, and it’s during the gap in immunity at about 9 weeks of age,1 that most kittens get FCoV from an infected mom.

FCoV is shed in feces, and shedding can persist for weeks, months or longer. Kittens get the virus by ingesting infected feces when they groom themselves or each another and from fomites, such as clothes, utensils and hands, which may carry the infection. Kittens start to shed FCoV in their feces a week after being infected.

Infection with FCoV causes inflammation of the intestines, but most cats don’t show any symptoms. Sometimes cats have brief episodes of diarrhea and/or mild sneezing, watery eyes and nasal discharge. Cats usually recover by producing antibodies against the virus within 7-10 days of infection. Some may be reinfected several times before they are 3 years old, shedding the virus on and off or continuously; some never shed the virus.

Detecting FCoV can be done by looking for viral DNA of FCoV in feces via a reverse transcriptase-polymerase chain reaction test (RT-PCR). However, single test results are unreliable because the virus may be shed intermittently or the cat may have been recently infected. As mentioned, most cats infected with FCoV eliminate the virus following infection.

Detecting FCoV can also be done by testing a blood sample for antibodies to FCoV. However, this test may be of little use since a positive result only indicates exposure to the virus; it doesn’t mean the cat currently has FCoV.

FCoV can survive indoors for up to 7 weeks under dry conditions, but is easily inactivated by most commercial disinfectants. Control and prevention of FCoV involves minimizing fecal contamination of the environment by providing adequate numbers of litter boxes, cleaning litter boxes daily, disinfecting litter boxes weekly and clipping/cleaning fur from the rear end of long-haired cats to minimize fecal debris accumulating there. Rooms, cages, bedding and litter boxes should be disinfected between groups of kittens/cats. In addition, before introducing new cats to a cattery or breeding program, the results of their FCoV blood test and fecal PRC test should be negative.

Why all this focus on FCoV? Because in approximately 10% of FCoV-infected cats the virus mutates, infects white blood cells and spreads throughout the body.2 When this happens, the virus is referred to as Feline Infectious Peritonitis Virus (FIPV). The body reacts to FIPV by mounting a strong inflammatory response around blood vessels and in the infected cells, often in the abdomen, kidney or brain. This interaction of the body’s own immune system, the FIP virus itself and how much exposure the cat had to FoCV, is responsible for the development of Feline Infectious Peritonitis (FIP). Since FIP is more common in related cats, there’s likely a genetic component as well in the development of FIP, and littermates of kittens that have developed FIP are at increased risk.

If FIP is present in a cattery, breeding facility or multi-cat household, removing persistently FCoV-infected and shedding cats can reduce the risk of FIP in that population. Multiple tests over an 8-month period are required to identify a chronically shedding carrier; five negative tests done at one-month intervals are required before a cat is considered non-shedding.3


  1. WINN FIP SYMPOSIUM: PURRsuing FIP and WINNing, p. 2
  2. Introduction to ABCD Guidelines on Feline Infectious Peritonitis (European Advisory Board on Cat Diseases: Video Interview with Diane Addie, PhD, BVMS, MRCVS)
  3. Feline Coronavirus (FCoV) RT-PCR (Animal Health Diagnostic Center, Cornell University College of Veterinary Medicine)

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